The nitrogen removal performance and microbial communities in a two-stage deep sequencing constructed wetland for advanced treatment of secondary effluent

The advanced treatment of secondary effluent was conducted in a two-stage deep sequencing constructed wetland (DSCW) which comprised a denitrification chamber (W1) and a nitrification chamber (W2). The results showed that a superior NO3−-N removal rate was observed in W1 with a C/N ratio of 6.5, and a high NH4+-N removal rate was obtained when the W2 was operated with 6-h duration of idle. In the long-term operation for 45 days, the two-stage DSCW pilot system achieved high and stable removal of TN, NH4+-N and NO3−-N, which were 92.9%, 83.7% and 95.6% in average, respectively. The microbial communities between W1 and W2 were significant different. Rich diversity of the microbial community and the high proportion of denitrifying bacteria in the W1 were essential for nitrogen removal in this treatment system. AOB in the W2 played a major role in NH4+-N removal in W2.